Our research program utilizes hemorrhagic hypotension as a condition during which the mirocirculation is substantially altered in comparison to normal function. Although hemorrhage provides a large change in a large number of parameters which may individually have an effect on small blood vessels, our hypothesis is that a limited number of parameters act to determine the responsiveness of small blood vessels to a large number of other variables. This project provides a direct quantitative investigation of the responses of small veins, postcapillary venules and their associated arteries and arteroles to hemorrhagic hypotension. These responses will be quantitated for subcutaneous microvasculature in the wings of unanesthetized bats (Myotis lucifugus) and for skeletal muscle microvasculature in the cremaster of rats anesthetized with urethane- chloralose or pentobarbital when these animals are exposed to reversible and irreversible hemorrhagic shock states. Data is acquired with closed-circuit television methods and reduced through digital computer techniques. In general, our current hypothesis focuses on the venules as a microcirculatory segment which is critically altered during hemorrhagic shock. At the present time, studies on the effect of anesthesia, hypoxia, hypercarbia, and pharmacological blockade on small arteries (90-120 microns) and veins (130-200 microns) are underway for the rat cremaster preparation. Bibliograahic references: Morff, R.J., D.L. Wiegman, M.J. Devaney, F.N. Miller, and P.D. Harris: A carotid sinus component in muscle microvascular responses to hypoxia. Fed. Proc. 34:461, 1975; Miller, F.N., D.L. Wiegman, M.J. Devaney, and P.D. Harris: Differential effects of TRIS on the vascular response to norepinphrine. World Congr. Microcirculation (Toronto, Canada), June 15, 1975.